Organic electroluminescent elements (so-called organic EL elements) utilizing the electroluminescence (hereinafter described as EL) of organic materials are thin film-type, completely solid elements that are capable of emitting light at low voltages of about several volts to several ten volts, and have many excellent characteristics such as high luminance, high luminescent efficiency, thin-type and light weight. Therefore, the organic electroluminescent elements have gained attentions in recent years as backlights for various displays, display boards such as signboards and emergency lamps, and plane emission bodies such as illumination light sources.
Such organic electroluminescent element has a constitution in which a luminescent layer constituted by using an organic material is sandwiched between two electrodes, and luminescent light generated in the luminescent layer transmits the electrode and is extracted outside of the electrode. Therefore, at least one of the two electrodes is constituted as a transparent electrode.
As the transparent electrode, oxide semiconductor-based materials such as indium tin oxide (SnO2—In2O3:Indium Tin Oxide:ITO) are generally used, and consideration aiming at decreasing resistance is also made by stacking ITO and silver (for example, see the following Patent Literatures 1 and 2). However, since ITO includes indium, which is a rare metal, the material cost is high, and it is necessary to conduct an annealing treatment at about 300° C. after the film formation so as to decrease the resistance. Therefore, a constitution in which a metal material having a high electroconductivity such as silver has been formed into a thin film, a constitution in which electroconductivity is ensured at a film thickness that is thinner than that of silver alone by mixing silver with aluminum (for example, see the following Patent Literature 3), and a constitution in which a light transmission property is ensured by providing a stacked structure in which a silver thin film layer is disposed on a primer layer formed of a metal other than silver (for example, see the following Patent Literature 4) are suggested.